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Malvic T.,INA Industry of Oil Plc.
Geoinformatics 2012 - 11th International Conference on Geoinformatics: Theoretical and Applied Aspects | Year: 2012

Successful artificial neural network analyses of the lithology data - prediction of either sandstones or shale were obtained. These were performed in the youngest (Pliocene, Pleistocene and Holocene) sediments in Sava Depression, Croatian part of the Pannonian Basin, and the input data was based on well log curves (spontaneous potential, shallow and deep resistivity curves). These analyses were successfully preformed in 20 wells of which in two, the training and validation of the networks was made. Such obtained lithology data was used for the construction of lithofacies maps which clearly show the distribution of the overall thickness of sandstone bodies and their number. Palaeotransport directions and areas with thicker sandstone interval for possible gas accumulations can also be observed in the constructed maps. The main influx of sediment was from the NE trough a channel which coincides with recent structural low defined by the absence of Pliocene outcrops while the thickest sandstone intervals can be delimited to the SW part of the mapping area.

Tomislav M.,University of Zagreb | Ana M.B.,INA Industry of Oil Plc.
Geologica Carpathica | Year: 2012

The Croatian part of the Pannonian Basin System includes several Miocene chronostratigraphic (sub)stages mostly characterized by weak permeable clastic sediments. They are often also mature source rocks at depths of more than 2500 m, from Late Badenian to Early Pannonian ages, represented by marls and calcitic marls, and kerogene Types II and III. The other types of weakly permeable sediments are tight sandstone mostly of Badenian age. Those two lithotypes are potential unconventional reservoirs described in the Bjelovar Subdepression, regarding their age, geological evolution, lithology, porosity and permeability. Domination of kerogene Type III and low total organic carbon defined marls as gas-bearing source rocks. Both marls and tight sandstones mostly have porosity less than 10 % and permeability less than 10-3 μm2. It is about 10-100 times lesser permeability than in conventional reservoirs. Weakly permeable zones are highly stochastically distributed and fluid flows are relatively short (several meters), which could be enhanced only by the using hydraulic or other fracturing techniques.

Malvic T.,INA Industry of Oil Plc. | Malvic T.,University of Zagreb | Velic J.,University of Zagreb
Petroleum Geoscience | Year: 2010

The Molve Field is the most important gas-condensate reservoir in Croatia. This petroleum system is not typical for the Pannonian System, because it comprises several reservoir lithologies, relatively high structural closure and significant tectonic influence on the field's compartmentalization. Strike-slip extension in the Middle Miocene and younger Late Miocene and Pliocene tectonics formed the present-day tectonic setting. Reservoir stratigraphy includes four lithofacies (from Devonian to Neogene) with a unique gas-water contact. The lithologies encompass cataclased granite, gneiss, schists, quartzites, dolomites, limestones and grainstones. Source rocks were generated in lacustrine organic facies and migration occurred in the Late Miocene to Pliocene. Reservoir gas includes 4.5-15.7% C2+, but also non-hydrocarbon components. Analysed porosity data were approximated with a normal-distribution curve in lithofacies I, II and III, making it possible to calculate mean and variance easily by descriptive statistics. Moreover, gas production and effective thicknesses generally can be linked through a linear trend. However, significant deviations in the expected increased production rate with regard to greater reservoir thickness are observed for particular wells. This is a result of locally abrupt changes in effective porosities and permeabilities, and the size of the drainage area along the main fault zones. These faults resulted in significant compartmentalization of the field. Furthermore, owing to significant facies variations, permeability and porosity gradually change, especially in the vertical direction. Significant reserves of condensate (3 106 m3) and gas (43 500 106 m3) with a high recovery rate of 71% make this field significant for geological reservoir models. The well-established geological model for this field and its stable high pressure have maintained production rates at a present level of approximately 2900 m3 gas and 165 m3 condensate per day, thus providing a valuable example for other large heterogeneous reservoirs in the Pannonian Basin. © 2010 EAGE/Geological Society of London.

Ivanisevic D.,Croatian Geological Survey | Malvic T.,INA Industry of Oil Plc. | Malvic T.,University of Zagreb
Journal of Maps | Year: 2015

The Pannonian Basin System (PBS) and associated parts of the surrounding orogens (SOs) were selected for a regional geochemical mapping of concentrations of potentially toxic metals, with the sample media the topsoil horizon. Geochemical data form a sample space that is different from Euclidean, and therefore standard statistical methods are not applicable for such data. To apply standard statistical methods, data were transformed to Euclidean space by using a special case of an isometric log-ratio transformation for a composition consisting of two parts (the first part is the metal concentration of interest; the second part is the total concentration of all other elements in the composition). Estimations were performed using deterministic (Ordinary Kriging) and stochastic (sequential Gaussian simulations (SGS)) methods. The resulting maps provide insight into the distribution of certain metals in the PBS and associated parts of the SOs, and are intended to serve as base maps for further studies. The maps obtained with SGS provide additional information on the variability (uncertainty) of estimation. © 2015 Danijel Ivanišević

Malvic T.,INA Industry of Oil Plc. | Malvic T.,University of Zagreb | Jovic G.,INA Industry of Oil Plc.
Journal of Maps | Year: 2012

The Kloštar Oil Field is situated at the north-western part of Sava Depression in the Croatian part of the Pannonian Basin. It is a typical geological structure that evolved through the Neogene and Quaternary and that is why the structural evolution is reconstructed using palinspastic mapping (i.e., using selected chronostratigraphic horizons as datum planes). The total map set includes six structural and 15 palaeostructural maps interpolated over five Elog markers and one border. The mapping has been performed using the Ordinary Kriging. The maps were used for the interpretation of geological evolution during the Neogene and Quaternary, and particularly a description of hydrocarbon reservoir formation and migration pathways. The structural development can be explained through two phases of transtension and two of transpression that existed regionally in the Sava Depression. However, the maps and cross-sections that are described locally show changes of dominant tectonic styles, particularly during the Quaternary when most of the field was a depositional centre. © 2012 Journal of Maps.

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